1. Field of the Invention
This invention relates to providing compound movement of an aeration unit, and more particularly, to first applying a primary force to an aeration unit of a water treatment apparatus to remove the aeration unit from the water treatment apparatus, and to second applying a secondary force to the aeration unit to move the entire aeration unit over a service area adjacent to the water treatment apparatus to facilitate servicing the aeration unit.
2. Discussion of Prior Aeration Unit Movers
Basins are used to purify liquids in facilities such as water and waste water treatment plants by removing impurities, thereby making the water suitable for use, reuse, or for further treatment. Aeration units are used in basins of the plants to provide gas for biological treatment, or for mixing the liquid. The aeration units are usually permanently installed in the basin. In many permanent installations, the pipes of the units are secured to the bottom of the basin to resist the inherent buoyancy of the pipes, which are filled with the gas. Thus, removal of the pipes for maintenance is difficult, if not impossible, without interrupting the aeration process.
Some have suggested the use of pipes with rotary joints to couple sections of the pipes together. In prior aeration units with removable pipes, the individual pipes and valves are generally difficult to handle. Where supports other than the bottom of the basin have been provided for the aeration units, hoists or cranes have been used to lift the supports. Such hoists or cranes often interfere with the aeration operations, and do not provide an easy way of repositioning the supports on the bottom so as to assure that the pipes of the aeration units are level during aeration operations. Further, the many different types of aeration units do not lend themselves to a universal, or all-purpose, way of retrieving the units from a basin for maintenance, and of replacing the units in the basin after maintenance with assurance that the pipes of the aeration unit will be level. Thus, there is a need for a way of retrieving from such basins all types of aeration units, including units that have already been installed, with a minimum of interference with ongoing aeration operations. Also, since plant operators are generally reluctant to increase investment just to maintain the existing aeration units, any new equipment for removal and replacement of existing aeration units must be as simple and cost-effective as possible.
The term "retrieval", and the term "retrieving", as used herein mean the removal of any type of aeration unit from such basin (e.g., for maintenance) and the movement of any such type of aeration unit into such basin, (e.g., following maintenance).
Other factors relating to maintenance of such aeration units include that, for efficient operation, controls for equipment that performs such retrieval, and preferably maintenance operations, should be centralized. Centralization, for example, means that the controls and the maintenance operations should be on the same one side of the basin, for ease of access by an operator or maintenance person.
An example of an attempt to retrieve one aerator pipe at a time from a basin is shown in Nordell U.S. Pat. No. 2,650,810. There, dual lengths of a single, main endless band extend parallel to each other along a coping at an edge of a basin. The coping extends above the pipe. At each of many spaced locations along the main band, separate cables are attached to the main band and extend around fixed pulleys secured to the coping. Each separate cable then extends down into the basin and is attached directly to a different part of the aeration pipe. As the main band is moved along the coping, one end of each separate cable moves with the main band, and the attached part of the cable moves up or down in the basin. With the attached part of each such cable attached to the aeration pipe, the cables move the aeration pipe up in the basin. This type of pipe moving system is provided for each aeration pipe. Further, it requires the two lengths of the main band to extend along the coping of the basin so that the separate cables may be attached to the main band and extend down into the basin so as to directly apply force to the pipe at locations spaced across the basin. Also, if an aeration pipe is centered in the basin, i.e. toward the center from the coping, a separate truss has to be mounted across the top of the basin to support the fixed pulleys which are normally secured to the coping when the pipe is directly below the coping. The extension of the main band across the coping of the basin, and such separate truss, may interfere with operations other than aeration.
In another method of moving a device for aerating liquid in a basin, shown in U.S. Pat. No. 2,144,385, a fixed rail is mounted in the basin for guiding sliders that carry pipe holders. The holders surround the pipe to avoid stressing the pipe. A cable pulls the sliders on the rail to move the pipe into and out of the basin. However, opposite ends of the cable exit the basin at opposite sides of the basin, such that there is no central point at which the cable is moved. Further, the pipe can only be removed in this manner if it is flexible.
Still another device for aerating liquid also requires use of a flexible, porous pipe for supplying the gas to the liquid. As described in U.S. Pat. No. 5,290,487, holders are fixed to the pipe, and the holders have sliders that ride on a rail attached to the bottom of the basin. The U.S. Pat. No. 5,290,487 patent describes problems encountered with such porous flexible pipe, holders, sliders and rails as including those caused by pulling on the pipe to cause the pipe to be guided into the basin by the sliders as they ride on the rail fixed to the floor of the basin. The force required to pull the pipe is said to stretch the pipe and distort the holes through which the gas is fed into the basin. Also, it is said that as the pipe is pulled, the sliders may jam on the rail, which may cause the pipe to break and require discontinuing operation of the basin to permit the rest of the pipe to be removed from the basin. The solution described in U.S. Pat. No. 5,290,487 still uses rails secured to the bottom of the basin, and still uses flexible porous pipe. The pipe is not attached directly to the holders, but is free to slide relative to the holders. Also, a separate cable is fed through and attached to each of the sliders, such that force is applied directly to each slider by the cable and not by the pipe. Despite these features, for removal of the pipe, the system described in U.S. Pat. 5,290,487 still requires the sliders to ride on the rails while the sliders are in the basin and located in the sludge that settles at the bottom of the basin. As a result, there is still the possibility that the sliders will jam on the rail during an attempt to remove the pipe from the basin. Further, to allow removal of the pipe from the basin, the pipe must still be flexible to allow it to bend at the bottom corner of the basin as it is pulled up out of the basin. Therefore, the system is not applicable to aeration units that use non-porous, rigid pipes.
In another device for aerating liquid in a basin, shown in U.S. Pat. No. 2,328,655, pipes supply air to manifolds in the basin. The pipes are provided with elbows having two sections which rotate to permit the pipes to swing and move out of the basin, carrying the manifolds out of the basin. However, to permit the pipes to clear a stantion of the basin, the swinging method of removing the pipes from the basin limits the length of the pipes.
In another version of a device for aerating liquid in a basin is shown in U.S. Pat. No. 1,195,067. There, no provision is made for removing a rotating pipe or a reciprocating pipe from the basin, other than manually lifting the pipes from the basin.
Sinner et al. U.S. Pat. No. 2,589,882 does not describe a system for moving an aeration unit. Rather, a casket lowering system uses two cables to allow the casket to move down under the force of gravity. The Sinner et al. system includes a fixed carriage that extends across the length and width of an open grave to support pulleys. A reel on the carriage at one end of the grave pays out two separate pairs of cables. One cable extends from the reel, around pulleys on the fixed carriage, and under one end of the casket. The other cable extends from the reel, around other pulleys on the carriage, and under the other end of the casket. As the reel is rotated, the cables pay out uniformly so that both ends of the casket are lowered at the same time. However, in addition to not being designed for moving an aeration unit, the Sinner et al. system requires that the fixed carriage extend all the way across the open grave to position both of the cables under the casket. Further, the carriage is not moved for moving the casket. Rather, the carriage only supports the reel and the pulleys, and both cables pass under the casket. Thus, Sinner et al. do not provide for one cable to move one end of a beam of a frame, and do not transfer force from one end of a movable frame to a second cable to lift an opposite end of the frame.
Applicants' previous system described in the above-referenced parent application provided structure and methods for retrieving an aeration unit from a basin of a water treatment apparatus in a primary which force is applied to the aeration unit from only one side of the basin of the water treatment apparatus. Part of such primary force was vector transferred from one end of a beam of the aeration unit to the other end of the beam to move both ends of the beam. The beam supported pipes of the aeration unit. A force transfer module included one force transfer strand held in a force transfer path between fixed opposite ends of the strand. The force transfer path extended in part along the beam, which was placed in compression during the force transfer. Motion of the one end of the beam resulting from the primary force (e.g., upward or downward motion) was vector transferred by the single force transfer strand to the opposite end of the beam so that both ends of the beam moved in the same upward or downward direction relative to the basin under the action of the primary force.